Effects of soil on the development, survival, and oviposition of Culex quinquefasciatus (Diptera: Culicidae) mosquitoes.

BACKGROUND: Water quality is known to influence the development and survival of larval mosquitoes, which affects mosquito-borne pathogen transmission as a function of the number of mosquitoes that reach adulthood and blood feed. Although water properties are known to affect mosquito development, few studies have investigated the link among soil properties, water quality, and mosquito development. Given the large number of ground-breeding mosquito species, this linkage is a potentially important factor to consider in mosquito ecology. In this study, we explored the effects of different soils on multiple life history parameters of the ground-breeding mosquito species Culex quinquefasciatus (Diptera: Culicidae). METHODS: Cx. quinquefasciatus larvae were reared in water combined with different soil substrates (sandy, silt, or clay loam textures) at increasing soil to water volume ratios, with and without the addition of organic matter (fish food). Gravid mosquitoes were offered different soil-water extracts to investigate soil effects on oviposition preference. RESULTS: Without the addition of organic matter, larval survival and development differed significantly among waters with different soil textures and volumes of substrate. Mosquitoes in water with clay loam soil survived longer and developed further than mosquitoes in other soil waters. Larvae survived for longer periods of time with increased volumes of soil substrate. Adding organic matter reduced the differences in larval survival time, development, and pupation among soil-water extracts. Adult female mosquitoes oviposited more frequently in water with clay loam soil, but the addition of organic matter reduced the soil effects on oviposition preference. CONCLUSIONS: This study suggests soil composition affects larval mosquito survival and development, as well as the oviposition preference of gravid females. Future studies could differentiate abiotic and biotic soil features that affect mosquitoes and incorporate soil variation at the landscape scale into models to predict mosquito population dynamics and mosquito-borne pathogen transmission.

A Plant-Fungus Bioassay Supports the Classification of Quinoa (Chenopodium quinoa Willd.) as Inconsistently Mycorrhizal.

Quinoa (Chenopodium quinoa Willd.) is becoming an increasingly important food crop. Understanding the microbiome of quinoa and its relationships with soil microorganisms may improve crop yield potential or nutrient use efficiency. Whether quinoa is a host or non-host of a key soil symbiont, arbuscular mycorrhizal fungi (AMF), is suddenly up for debate with recent field studies reporting root colonization and presence of arbuscules. This research seeks to add evidence to the mycorrhizal classification of quinoa as we investigated additional conditions not previously explored in quinoa that may affect root colonization. A greenhouse study used six AMF species, two AMF commercial inoculant products, and a diverse set of 10 quinoa genotypes. Results showed 0 to 3% quinoa root colonization by AMF when grown under greenhouse conditions. Across quinoa genotypes, AMF inoculant affected shoot dry weight (p = 0.066) and height (p = 0.031). Mykos Gold produced greater dry biomass than Claroideoglomus eutunicatum (27% increase), Rhizophagus clarus (26% increase), and within genotype CQ119, the control (21% increase). No treatment increased plant height compared to control, but Funneliformis mosseae increased height compared to C. eutunicatum (25% increase) and Rhizophagus intraradices (25% increase). Although quinoa plants were minimally colonized by AMF, plant growth responses fell along the mutualism-parasitism continuum. Individual AMF treatments increased leaf greenness in quinoa genotypes 49ALC and QQ87, while R. clarus decreased greenness in CQ119 compared to the control. Our research findings support the recommendation to classify quinoa as non-mycorrhizal when no companion plant is present and inconsistently mycorrhizal when conditional colonization occurs.

Organic Farming Sharpens Plant Defenses in the Field.

Plants deploy a variety of chemical and physical defenses to protect themselves against herbivores and pathogens. Organic farming seeks to enhance these responses by improving soil quality, ultimately altering bottom up regulation of plant defenses. While laboratory studies suggest this approach is effective, it remains unclear whether organic agriculture encourages more-active plant defenses under real-world conditions. Working on the farms of cooperating growers, we examined gene expression in the leaves of two potato (Solanum tuberosum) varieties, grown on organic vs. conventional farms. For one variety, Norkotah, we found significantly heightened initiation of genes associated with plant-defense pathways in plants grown in organic vs. conventional fields. Organic Norkotah fields exhibited lower levels of nitrate in soil and of nitrogen in plant foliage, alongside differences in communities of soil bacteria, suggesting possible links between soil management and observed differences in plant defenses. Additionally, numbers of predatory and phloem-feeding insects were higher in organic than conventional fields. A second potato variety, Alturas, which is generally grown using fewer inputs and in poorer-quality soils, exhibited lower overall herbivore and predator numbers, few differences in soil ecology, and no differences in gene-activity in organic and conventional farming systems. Altogether, our results suggest that organic farming has the potential to increase plants' resistance to herbivores, possibly facilitating reduced need for insecticide applications. These benefits appear to be mediated by plant variety and/or farming context.

In situ degradation of biodegradable plastic mulch films in compost and agricultural soils.

The global use of agricultural plastic films, which provide multiple benefits for food production, is expected to grow by 59% from 2018 to 2026. Disposal options for agricultural plastics are limited and a major global concern, as plastic fragments from all sources ultimately accumulate in the sea. Biodegradable plastic mulches could potentially alleviate the disposal problem, but little is known about how well they degrade under different environmental conditions. We quantified the degradation of biodegradable plastic mulches in compost and in soil at warm and cool climates (Tennessee and Washington). Mulch degradation was assessed by Fourier-transformed infrared (FTIR) spectroscopy, molecular weight analysis, thermogravimetric analysis (TGA), nuclear-magnetic resonance (NMR), and mulch surface-area quantification. Biodegradable plastic mulches degraded faster in compost than in soil: degradation, as assessed by surface-area reduction, in compost ranged from 85 to 99% after 18 weeks, and in soil from 61 to 83% in Knoxville and 26 to 63% in Mount Vernon after 36 months. FTIR analyses indicate that hydrolytic degradation of ester bonds occurred, and a significant reduction of molecular weight was observed. TGA and NMR confirmed degradation of biodegradable polymers. Our results indicate that biodegradable plastic mulches degrade in soil, but at different rates in different climates and that degradation occurs over several years. Faster degradation occurred in compost, making composting a viable disposal method, especially in cool climates, where mulch fragments in soil may persist for many years.

Landscape context affects the sustainability of organic farming systems.

Organic agriculture promotes sustainability compared to conventional agriculture. However, the multifunctional sustainability benefits of organic farms might be mediated by landscape context. Assessing how landscape context affects sustainability may aid in targeting organic production to landscapes that promote high biodiversity, crop yields, and profitability. We addressed this using a meta-analysis spanning 60 crop types on six continents that assessed whether landscape context affected biodiversity, yield, and profitability of organic vs. conventional agroecosystems. We considered landscape metrics reflecting landscape composition (percent cropland), compositional heterogeneity (number and diversity of cover types), and configurational heterogeneity (spatial arrangement of cover types) across our study systems. Organic sites had greater biodiversity (34%) and profits (50%) than conventional sites, despite lower yields (18%). Biodiversity gains increased as average crop field size in the landscape increased, suggesting organic farms provide a "refuge" in intensive landscapes. In contrast, as crop field size increased, yield gaps between organic and conventional farms increased and profitability benefits of organic farming decreased. Profitability of organic systems, which we were only able to measure for studies conducted in the United States, varied across landscapes in conjunction with production costs and price premiums, suggesting socioeconomic factors mediated profitability. Our results show biodiversity benefits of organic farming respond differently to landscape context compared to yield and profitability benefits, suggesting these sustainability metrics are decoupled. More broadly, our results show that the ecological, but not the economic, sustainability benefits of organic agriculture are most pronounced in more intensive agricultural landscapes.

Effects of restricting movement between root and canopy populations of woolly apple aphid.

Movement of insect pests between spatially subdivided populations can allow them to recolonize areas where local extinction has occurred, increasing pest persistence. Populations of woolly apple aphid (Eriosoma lanigerum [Hausmann]; Hemiptera: Aphididae), a worldwide pest of apple (Malus domestica [Borkhausen]), occur both below- and aboveground. These spatially subdivided subpopulations encounter different abiotic conditions, natural enemies, and control tactics. Restricting movement between them might be an effective management tactic to decrease woolly apple aphid persistence and abundance. We examined this possibility in the field, using sticky barriers to restrict upward woolly apple aphid movement to tree canopies, and in the greenhouse, using mulches and sand amendments to restrict downward movement to roots. In the field, blocking aphid movement up tree trunks did not decrease the number of colonies in tree canopies. Instead, sticky-banded apple trees had higher aphid colony counts late in the study. Earwigs, which are woolly apple aphid predators, were excluded from tree canopies by sticky bands. In the greenhouse, fewer root galls (indicative of aphid feeding) occurred on trees in sandy potting media and on those with mulch (wood chips or paper slurry). Our results suggest that upward movement is less important than other factors that affect aboveground aerial woolly apple aphid population dynamics. In addition, apple orchards planted in sandier soils or with mulches may be partially protected from woolly apple aphid root feeding.

Bacteria and Competing Herbivores Weaken Top-Down and Bottom-Up Aphid Suppression.

Herbivore suppression is mediated by both plant defenses and predators. In turn, plant defenses are impacted by soil fertility and interactions with soil bacteria. Measuring the relative importance of nutritional and microbial drivers of herbivore resistance has proven problematic, in part because it is difficult to manipulate soil-bacterial community composition. Here, we exploit variation in soil fertility and microbial biodiversity across 20 farms to untangle suppression of aphids (Brevicoryne brassicae) through bottom-up and top-down channels. We planted Brassica oleracea plants in soil from each farm, manipulated single and dual infestations of aphids alone or with caterpillars (Pieris rapae), and exposed aphids to parasitoid wasps (Diaeretiella rapae) in the open field. We then used multi-model inference to identify the strongest soil-based predictors of herbivore growth and parasitism. We found that densities of Bacillus spp., a genus known to include plant-growth-promoting rhizobacteria, negatively correlated with aphid suppression by specialist parasitoids. Aphid parasitism also was disrupted on plants that had caterpillar damage, compared to plants attacked only by aphids. Relative abundance of Pseudomonas spp. bacteria correlated with higher aphid growth, although this appeared to be a direct effect, as aphid parasitism was not associated with this group of bacteria. Non-pathogenic soil bacteria are often shown to deliver benefits to plants, improving plant nutrition and the deployment of anti-herbivore defenses. However, our results suggest that these plant growth-promoting bacteria may also indirectly weaken top-down aphid suppression by parasitoids and directly improve aphid performance. Against a background of varying soil fertility, microbial biodiversity, competing herbivores, and natural enemies, we found that effects of non-pathogenic soil microbes on aphid growth outweighed those of nutritional factors. Therefore, predictions about the strength of plant defenses along resource gradients must be expanded to include microbial associates.

Dung beetle-mediated soil modification: a data set for analyzing the effects of a recent introduction on soil quality.

Globally, dung beetles (Scarabaeidae: Scarabaeinae) are linked to many critical ecosystem processes involving the consumption and breakdown of mammal dung. Due to New Zealand's unique evolutionary history, resulting from its geographic isolation from Gondwana, endemic dung-dwelling fauna evolved in the absence of large mammals. Europeans introduced livestock to the islands in the late 18th and 19th centuries, resulting in a buildup of undecomposed feces and unrecycled nutrients due to the absence of dung beetles. To mitigate this situation, in 2011, the New Zealand Environmental Protection Agency approved the release of 11 species of exotic beetles with the expectation that these insects would fulfill a critically missing link in converting aboveground manure biomass into higher quality soils belowground. Widespread releases began in 2014. To enable others in the future to test the environmental impacts of the beetle introductions, we present a detailed characterization of soil physical, chemical, and biological properties, shortly after the initial and intentional introduction of dung beetles to 16 release sites across both the North and South Islands of New Zealand. As beetle populations become established, these baseline data will enable quantification of the degree to which different exotic dung beetle communities can modify soils, specifically if they facilitate soil nutrient cycling. There are no copyright or proprietary restrictions for research or teaching purposes. Usage of the data set must be cited by referencing this publication.

Dual-guild herbivory disrupts predator-prey interactions in the field.

Plant defenses often mediate whether competing chewing and sucking herbivores indirectly benefit or harm one another. Dual-guild herbivory also can muddle plant signals used by specialist natural enemies to locate prey, further complicating the net impact of herbivore-herbivore interactions in naturally diverse settings. While dual-guild herbivore communities are common in nature, consequences for top-down processes are unclear, as chemically mediated tri-trophic interactions are rarely evaluated in field environments. Combining observational and experimental approaches in the open field, we test a prediction that chewing herbivores interfere with top-down suppression of phloem feeders on Brassica oleracea across broad landscapes. In a two-year survey of 52 working farm sites, we found that parasitoid and aphid densities on broccoli plants positively correlated at farms where aphids and caterpillars rarely co-occurred, but this relationship disappeared at farms where caterpillars commonly co-occurred. In a follow-up experiment, we compared single and dual-guild herbivore communities at four local farm sites and found that caterpillars (P. rapae) caused a 30% reduction in aphid parasitism (primarily by Diaeretiella rapae), and increased aphid colony (Brevicoryne brassicae) growth at some sites. Notably, in the absence of predators, caterpillars indirectly suppressed, rather than enhanced, aphid growth. Amid considerable ecological noise, our study reveals a pattern of apparent commensalism: herbivore-herbivore facilitation via relaxed top-down suppression. This work suggests that enemy-mediated apparent commensalism may override constraints to growth induced by competing herbivores in field environments, and emphasizes the value of placing chemically mediated interactions within their broader environmental and community contexts.

Organic agriculture in the twenty-first century.

Organic agriculture has a history of being contentious and is considered by some as an inefficient approach to food production. Yet organic foods and beverages are a rapidly growing market segment in the global food industry. Here, we examine the performance of organic farming in light of four key sustainability metrics: productivity, environmental impact, economic viability and social wellbeing. Organic farming systems produce lower yields compared with conventional agriculture. However, they are more profitable and environmentally friendly, and deliver equally or more nutritious foods that contain less (or no) pesticide residues, compared with conventional farming. Moreover, initial evidence indicates that organic agricultural systems deliver greater ecosystem services and social benefits. Although organic agriculture has an untapped role to play when it comes to the establishment of sustainable farming systems, no single approach will safely feed the planet. Rather, a blend of organic and other innovative farming systems is needed. Significant barriers exist to adopting these systems, however, and a diversity of policy instruments will be required to facilitate their development and implementation.

Financial competitiveness of organic agriculture on a global scale.

To promote global food and ecosystem security, several innovative farming systems have been identified that better balance multiple sustainability goals. The most rapidly growing and contentious of these systems is organic agriculture. Whether organic agriculture can continue to expand will likely be determined by whether it is economically competitive with conventional agriculture. Here, we examined the financial performance of organic and conventional agriculture by conducting a meta-analysis of a global dataset spanning 55 crops grown on five continents. When organic premiums were not applied, benefit/cost ratios (-8 to -7%) and net present values (-27 to -23%) of organic agriculture were significantly lower than conventional agriculture. However, when actual premiums were applied, organic agriculture was significantly more profitable (22-35%) and had higher benefit/cost ratios (20-24%) than conventional agriculture. Although premiums were 29-32%, breakeven premiums necessary for organic profits to match conventional profits were only 5-7%, even with organic yields being 10-18% lower. Total costs were not significantly different, but labor costs were significantly higher (7-13%) with organic farming practices. Studies in our meta-analysis accounted for neither environmental costs (negative externalities) nor ecosystem services from good farming practices, which likely favor organic agriculture. With only 1% of the global agricultural land in organic production, our findings suggest that organic agriculture can continue to expand even if premiums decline. Furthermore, with their multiple sustainability benefits, organic farming systems can contribute a larger share in feeding the world.

Utility of metabolomics toward assessing the metabolic basis of quality traits in apple fruit with an emphasis on antioxidants.

A gas chromatography-mass spectrometry approach was employed to evaluate the use of metabolite patterns to differentiate fruit from six commercially grown apple cultivars harvested in 2008. Principal component analysis (PCA) of apple fruit peel and flesh data indicated that individual cultivar replicates clustered together and were separated from all other cultivar samples. An independent metabolomics investigation with fruit harvested in 2003 confirmed the separate clustering of fruit from different cultivars. Further evidence for cultivar separation was obtained using a hierarchical clustering analysis. An evaluation of PCA component loadings revealed specific metabolite classes that contributed the most to each principal component, whereas a correlation analysis demonstrated that specific metabolites correlate directly with quality traits such as antioxidant activity, total phenolics, and total anthocyanins, which are important parameters in the selection of breeding germplasm. These data sets lay the foundation for elucidating the metabolic basis of commercially important fruit quality traits.

Effective monitoring of agriculture: a response.

The development of effective agricultural monitoring networks is essential to track, anticipate and manage changes in the social, economic and environmental aspects of agriculture. We welcome the perspective of Lindenmayer and Likens (J. Environ. Monit., 2011, 13, 1559) as published in the Journal of Environmental Monitoring on our earlier paper, "Monitoring the World's Agriculture" (Sachs et al., Nature, 2010, 466, 558-560). In this response, we address their three main critiques labeled as 'the passive approach', 'the problem with uniform metrics' and 'the problem with composite metrics'. We expand on specific research questions at the core of the network design, on the distinction between key universal and site-specific metrics to detect change over time and across scales, and on the need for composite metrics in decision-making. We believe that simultaneously measuring indicators of the three pillars of sustainability (environmentally sound, social responsible and economically viable) in an effectively integrated monitoring system will ultimately allow scientists and land managers alike to find solutions to the most pressing problems facing global food security.

Fruit and soil quality of organic and conventional strawberry agroecosystems.

BACKGROUND: Sale of organic foods is one of the fastest growing market segments within the global food industry. People often buy organic food because they believe organic farms produce more nutritious and better tasting food from healthier soils. Here we tested if there are significant differences in fruit and soil quality from 13 pairs of commercial organic and conventional strawberry agroecosystems in California. METHODOLOGY/PRINCIPAL FINDINGS: At multiple sampling times for two years, we evaluated three varieties of strawberries for mineral elements, shelf life, phytochemical composition, and organoleptic properties. We also analyzed traditional soil properties and soil DNA using microarray technology. We found that the organic farms had strawberries with longer shelf life, greater dry matter, and higher antioxidant activity and concentrations of ascorbic acid and phenolic compounds, but lower concentrations of phosphorus and potassium. In one variety, sensory panels judged organic strawberries to be sweeter and have better flavor, overall acceptance, and appearance than their conventional counterparts. We also found the organically farmed soils to have more total carbon and nitrogen, greater microbial biomass and activity, and higher concentrations of micronutrients. Organically farmed soils also exhibited greater numbers of endemic genes and greater functional gene abundance and diversity for several biogeochemical processes, such as nitrogen fixation and pesticide degradation. CONCLUSIONS/SIGNIFICANCE: Our findings show that the organic strawberry farms produced higher quality fruit and that their higher quality soils may have greater microbial functional capability and resilience to stress. These findings justify additional investigations aimed at detecting and quantifying such effects and their interactions.

Monitoring the world's agriculture.

To feed the world without further damaging the planet, Jeffrey Sachs and 24 foodsystem experts call for a global data collection and dissemination network to track the myriad impacts of different farming practices.